Known in the present state of the art is a vibratory pipe wrench (cf., e.g., USSR Inventor's Certificate No. 647,103, Int. Cl. B25B 13/50, priority of Feb. 14, 1977, published Feb. 15, 1979 in the "Bulletin of discoveries, inventions, industrial designs and trade marks", No. 6, p. 39 (in Russian), which comprises a hollow handle with a vibrator and a fit-on movable jaw. The vibrator is located in the handle interior and has a gripping jaw, which is essentially a tip of a wear-resistant material designed to be in contact with the pipe being turned up.
The vibrator is made of a piezoelectric material and is electrically connected to a generator to establish elastic vibrations therein, which are imparted to the pipe in the form of impacts directed at an acute angle to the pipe surface. The vibrator rests upon supports made from a low-elastic material, such as rubber, so as to prevent vibrator oscillations from penetrating into the handle.
The fit-on movable jaw is articulated to the handle and is provided with two rollers which grip the pipe and serve also as stops.
However, the aforediscussed vibratory pipe wrench features but low operating reliability due to a possible breakage of the vibrator (made from such a brittle material as piezoceramics) when the wrench is overstrained by the operator.
Moreover, the torque developed by the vibrator is oftentimes inadequate to finally tighten the thread joint. This is because the torque is proportionate to the amplitude of the vibrator oscillations, while said amplitude is restricted to too low a value.
Furthermore, when the vibratory pipe wrench in question operates on an idle run, i.e., the vibrator gripping jaw does not contact the pipe being handled and relays no impact energy to the pipe, the amplitude of the vibrator oscillations and hence the varying mechanical stresses therein will be much higher than those in the course of operation under load when the vibrator gripping jaw contacts the pipe being handled and part of acoustic energy is imparted to the pipe. Since the maximum mechanical stresses in the vibrator developed during the idle-run operation should not exceed the permissible stress value of the material the vibrator is made from, the varying stresses and hence the torque developed during operation under load, that is, during the pipe rotation, will be much lower than those maximum attainable with a given construction.
In addition, in case of considerable amplitudes of the vibrator oscillations the latter grows overheated due to electrical and mechanical losses therein, which places further restrictions upon the torque magnitude developed by the known vibratory pipe tongs.
And last but not least, the vibrator resonant frequency is liable to vary in the course of operation depending upon the degree of wear on the gripping jaw thereof and upon the altering force of its pressure against the pipe. This, in turn, necessitates permanent readjustment of the generator frequency which complicates the operation of the known vibratory pipe wrench.